Model-based rotor speed keep out zone control

ABSTRACT

A system for keep out zone control includes a gas turbine engine and a controller operable to determine a closing threshold with respect to an upper limit and an opening threshold with respect to a lower limit of a movement range of an effector of the gas turbine engine based on an on-board model, where the upper limit and the lower limit define a keep out zone of a target parameter of the gas turbine engine. The controller determines a projected state of the target parameter absent a correction command to the effector, applies a closing correction to the effector based on determining that the projected state of the target parameter would result in being above the closing threshold, and applies an opening correction to the effector based on determining that the projected state of the target parameter would result in being below the opening threshold.

BACKGROUND

The subject matter disclosed herein generally relates to rotatingmachinery and, more particularly, to a method and an apparatus formodel-based rotor speed keep out zone control for a gas turbine engine.

Gas turbine engines typically include multiple spools or rotors thatconnect compressor sections with turbine sections. For example, in atwo-spool configuration, a low spool can include a rotor with lowpressure compressor and low pressure turbine sections, and a high spoolcan include a rotor with high pressure compressor and high pressureturbine sections. Gas turbine engine controls typically attempt tocontrol the speed of the low spool responsive to a command, such as apilot thrust control. As the low spool speed is adjusted to meet thecommand, the high spool speed “floats” relative to the low spool speed.For example, as the low spool speed increases due to increased fuelconsumption, the high spool speed also increases in response to theincreased fuel consumption. The corresponding speed of the high spoolmay not be directly controlled but has known relationships relative thelow spool speed and other operating parameters.

As the low and high spool speeds change, there may be speed ranges inwhich engine components experience increased wear. Dwelling in speedranges that are known to exacerbate wear may reduce engine componentlife.

BRIEF DESCRIPTION

According to one embodiment, a system for keep out zone control includesa gas turbine engine including at least one compressor section and atleast one turbine section operably coupled to a shaft of a spool. Thesystem also includes a controller is operable to determine a closingthreshold with respect to an upper limit and an opening threshold withrespect to a lower limit of a movement range of an effector of the gasturbine engine based on an on-board model, where the upper limit and thelower limit define a keep out zone of a target parameter of the gasturbine engine. The controller is also operable to determine a projectedstate of the target parameter of the gas turbine engine absent acorrection command to the effector, apply a closing correction to theeffector as the correction command based on determining that theprojected state of the target parameter of the gas turbine engine wouldresult in being above the closing threshold, and apply an openingcorrection to the effector as the correction command based ondetermining that the projected state of the target parameter of the gasturbine engine would result in being below the opening threshold.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the closingthreshold and the opening threshold define a switch hysteresis band, andthe upper limit and the lower limit define a keep out zone width withrespect to the target parameter of the gas turbine engine.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the spool is ahigh speed spool, and the gas turbine engine further includes a lowspeed spool, where the low speed spool includes a low pressurecompressor section and a low pressure turbine section.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the targetparameter is a speed of the high speed spool, and the effector is a highpressure compressor stator vane actuator.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the controlleris further configured to select between the closing correction and theopening correction based on comparing the projected state of the targetparameter with the closing threshold and the opening threshold todetermine the correction command, and add the correction command to ahigh pressure compressor stator vane schedule to control a position of aplurality of high pressure compressor stator vanes using the highpressure compressor stator vane actuator.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the correctioncommand is rate limited, and the closing correction and the openingcorrection are range limited.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the controlleris further configured to determine an adder authority as an adder valueto define the upper limit and the lower limit based on at least onespeed and at least one vane angle of the gas turbine engine, and splitthe adder value between an opening direction and a closing direction ofthe effector.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the closingthreshold and the opening threshold are determined with respect to theadder value, a change rate of the at least one speed, and a change rateof the at least one vane angle.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the projectedstate of the target parameter is determined based on a value of the atleast one speed, the adder value, the change rate of the at least onespeed, and the change rate of the at least one vane angle.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include where the controlleris further configured to apply a closing keep out zoneproportional-integral control to the target parameter with respect tothe upper limit to determine the closing correction, and apply anopening keep out zone proportional-integral control to the targetparameter with respect to the lower limit to determine the openingcorrection.

According to an embodiment, a method for keep out zone control in a gasturbine engine includes determining a closing threshold with respect toan upper limit and an opening threshold with respect to a lower limit ofa movement range of an effector of the gas turbine engine based on anon-board model, wherein the upper limit and the lower limit define akeep out zone of a target parameter of the gas turbine engine,determining a projected state of the target parameter of the gas turbineengine absent a correction command to the effector, applying a closingcorrection to the effector as the correction command based ondetermining that the projected state of the target parameter of the gasturbine engine would result in being above the closing threshold, andapplying an opening correction to the effector as the correction commandbased on determining that the projected state of the target parameter ofthe gas turbine engine would result in being below the openingthreshold.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include selecting between theclosing correction and the opening correction based on comparing theprojected state of the target parameter with the closing threshold andthe opening threshold to determine the correction command, and addingthe correction command to a high pressure compressor stator vaneschedule to control a position of a plurality of high pressurecompressor stator vanes using the high pressure compressor stator vaneactuator.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include determining an adderauthority as an adder value to define the upper limit and the lowerlimit based on at least one speed and at least one vane angle of the gasturbine engine, and splitting the adder value between an openingdirection and a closing direction of the effector.

In addition to one or more of the features described above or below, oras an alternative, further embodiments may include applying a closingkeep out zone proportional-integral control to the target parameter withrespect to the upper limit to determine the closing correction, andapplying an opening keep out zone proportional-integral control to thetarget parameter with respect to the lower limit to determine theopening correction.

A technical effect of the apparatus, systems and methods is achieved byperforming model-based rotor speed keep out zone control for a gasturbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a partial cross-sectional illustration of a gas turbineengine, in accordance with an embodiment of the disclosure;

FIG. 2 is a schematic diagram of a control system of a gas turbineengine, in accordance with an embodiment of the disclosure;

FIG. 3 is a block diagram of a model-based controller for rotor speedkeep out zone control, in accordance with an embodiment of thedisclosure;

FIG. 4 is a chart illustrating control system thresholds, in accordancewith an embodiment of the disclosure; and

FIG. 5 is a flow chart illustrating a method, in accordance with anembodiment of the disclosure.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct, while the compressorsection 24 drives air along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a two-spool turbofan gasturbine engine in the disclosed non-limiting embodiment, it should beunderstood that the concepts described herein are not limited to usewith two-spool turbofans as the teachings may be applied to other typesof turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through aspeed change mechanism, which in exemplary gas turbine engine 20 isillustrated as a geared architecture 48 to drive the fan 42 at a lowerspeed than the low speed spool 30. The high speed spool 32 includes anouter shaft 50 that interconnects a high pressure compressor 52 and highpressure turbine 54. A combustor 56 is arranged in exemplary gas turbine20 between the high pressure compressor 52 and the high pressure turbine54. An engine static structure 36 is arranged generally between the highpressure turbine 54 and the low pressure turbine 46. The engine staticstructure 36 further supports bearing systems 38 in the turbine section28. The inner shaft 40 and the outer shaft 50 are concentric and rotatevia bearing systems 38 about the engine central longitudinal axis Awhich is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion. It will be appreciated that each of the positions of the fansection 22, compressor section 24, combustor section 26, turbine section28, and fan drive gear system 48 may be varied. For example, gear system48 may be located aft of combustor section 26 or even aft of turbinesection 28, and fan section 22 may be positioned forward or aft of thelocation of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present disclosure isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,688 meters). The flight condition of 0.8 Mach and35,000 ft (10,688 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]{circumflex over( )}0.5. The “Low corrected fan tip speed” as disclosed herein accordingto one non-limiting embodiment is less than about 1150 ft/second (350.5m/sec).

While the example of FIG. 1 illustrates one example of the gas turbineengine 20, it will be understood that any number of spools, inclusion oromission of the gear system 48, and/or other elements and subsystems arecontemplated. Further, rotor systems described herein can be used in avariety of applications and need not be limited to gas turbine enginesfor aircraft applications. For example, rotor systems can be included inpower generation systems, which may be ground-based as a fixed positionor mobile system, and other such applications.

FIG. 2 illustrates a control system 200 of the gas turbine engine 20 ofFIG. 1. The control system 200 includes a plurality of sensors 220, suchas speed sensors, temperature sensors, strain sensors, pressure sensors,and other sensor types known in the art that can be distributedthroughout the gas turbine engine 20. A fuel control unit 222 can meterthe flow of fuel to the combustor 56 of FIG. 1 to increase or decreasethe speed of the low speed spool 30 and the high speed spool 32 ofFIG. 1. The control system 200 also includes a plurality of effectors224, such as one or more of a low pressure compressor bleed valveactuator 226, a low pressure compressor stator vane actuator 228, a highpressure compressor stator vane actuator 230, an active clearancecontrol actuator 232, and other such effectors.

A controller 256 can interface with the sensors 220, fuel control unit222, effectors 224, and/or other components (not depicted) of the gasturbine engine 20 of FIG. 1. In embodiments, the controller 256 cancontrol and monitor for fault conditions of the gas turbine engine 20.For example, the controller 256 can be a full authority digital enginecontrol (FADEC) of the gas turbine engine 20. In embodiments, thecontroller 256 can include a processing system 260, a memory system 262,and an input/output interface 264. The controller 256 can also includevarious operational controls, such as a model-based keep out zonecontrol 266 that controls one or more of the effectors 224 as furtherdescribed herein.

The processing system 260 can include any type or combination of centralprocessing unit (CPU), including one or more of: a microprocessor, adigital signal processor (DSP), a microcontroller, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), or the like. The memory system 262 can store data andinstructions that are executed by the processing system 260. Inembodiments, the memory system 262 may include random access memory(RAM), read only memory (ROM), or other electronic, optical, magnetic,or any other computer readable medium onto which is stored data andalgorithms in a non-transitory form. The input/output interface 264 isconfigured to collect sensor data from the sensors 220 and interfacewith various components and subsystems, such as components of the fuelcontrol unit 222, effectors 224, and/or other components (not depicted)of the gas turbine engine 20. The controller 256 provides a means forcontrolling the effectors 224 based on the model-based keep out zonecontrol 266 that is dynamically updated during operation of the gasturbine engine 20 of FIG. 1. The means for controlling the effectors 224can be otherwise subdivided, distributed, or combined with other controlelements.

Referring now to FIG. 3, a block diagram of a model-based controller 300is depicted, in accordance with an embodiment of the disclosure. Themodel-based controller 300 is an example of the model-based keep outzone control 266 and may be incorporated in the controller 256 of FIG.2. The model-based controller 300 can include an open/close decisionmaking logic 302, actuation controllers 304, final selection logic 306,and add control adjustments to nominal effector schedules 308. Theexample of FIG. 3 is described with respect to rotor speed (N2) of thehigh speed spool 32 as a target parameter of the gas turbine engine 20of FIG. 1 and the high pressure compressor stator vane actuator 230 ofFIG. 2 as an effector 224 to control; however, it will be understoodthat embodiments can apply to a variety of target parameters andeffectors 224 of the gas turbine engine 20 depending on the need toestablish keep out zones.

The open/close decision making logic 302 can define N2 keep out zonebounds at block 310, define vane adder authority at block 312, computethresholds for when to open/close high pressure compressor stator vanesdriven by the high pressure compressor stator vane actuator 230 at block314, compute a projected state of N2 in steady state that representswhat sensed N2 would be absent a correction command to the high pressurecompressor stator vane actuator 230 at block 316, and select theopen/close direction based on the projected state of N2 versusthresholds at block 318. The keep out zone bounds and thresholds areillustrated in chart 400 of FIG. 4 as an example for purposes ofexplanation. A threshold to switch 402 between opening and closing ofthe high pressure compressor stator vane actuator 230 can be defined interms of N2 values, for instance, at about half way between an upperlimit 404 and a lower limit 406 that define a keep out zone as N2 speedsto avoid or minimize time in range. The upper limit 404 and lower limit406 form a keep out zone width 408, where the high pressure compressorstator vane actuator 230 can either be adjusted to be more opened ormore closed than currently scheduled to shift the N2 speed higher orlower outside of the keep out zone. Hysteresis 410 can be added aroundthe threshold to switch 402 to avoid potential limit cycling. Thedecision to switch directions between opening and closing is made basedon the projected N2 (block 316) crossing a closing threshold 412 or anopening threshold 414. Further embodiments can have alternate controllaws with different design goals. For example, embodiments can minimizetime in a keep out zone (or set of keep out zones) while also minimizingthe control adder size to reduce changes to the nominal effectorschedule. This alternate approach can be performed by using model-basedcontrol information to set open\close thresholds and to define anaccurate projected target parameter to minimize activity. Model-basedkeep out zone control can prevent limit cycling in and out of a keep outzone using a projected target parameter, for instance, by knowing moreprecisely what the target parameter would be without correction.

The closing threshold 412 for N2 can be defined as δ_(C)×∂N2/∂HPC whereδ_(C) is a movement change in the closing direction and ∂N2/∂HPC is amodel-based partial derivative (k) that relates a change in N2 to achange in vane angle of the high pressure compressor 52 of FIG. 1. Theopening threshold 414 for N2 can be defined as δ_(O)×∂N2/∂HPC, whereδ_(O) is a movement change in the opening direction. The adder authorityof block 312 of FIG. 3 can be represented as δ_(ADDER)=δ_(C)+δ_(O),where the adder splits authority between closing and opening directions.As one example using a model-based partial derivative, the adder can becomputed as the keep out zone width 408 plus hysteresis 410 divided byk, which can be expressed as:

${{\partial N}\; 2\text{/}{\partial{HPC}}} = {{k\mspace{14mu}{and}\mspace{14mu}\delta_{ADDER}} = {\frac{\left( {{{KOZ}\mspace{14mu}{Width}} + {Hyst}} \right)}{k}.}}$As another example, model lookup of variables can be used, where k canbe determined as a function of a corrected N1 speed (n1c2) of the lowspeed spool 30 of FIG. 1 and a pressure ratio of P2 divided by Pambient, which can be expressed as: ∂N2/∂HPC=f(n1c2, P₂/P_(AMB)). Usinga lookup relative to ith and jth table entries, the adder can beexpressed as

$\delta_{ADDER} = {\frac{\left( {{{KOZ}\mspace{14mu}{Width}} + {Hyst}} \right)}{\left( {{\partial N}\; 2\text{/}{\partial{HPC}}} \right)_{i,j}}.}$Alternatively, a lookup function can be based on corrected N2 to a T25station value of N2C25. Embodiments can use model information to allowcontrol of a secondary effector (e.g., vane control rather than fuelcontrol) to affect a target parameter, such as N2, with negligibledisruption to thrust.

Returning to FIG. 3 and with continued reference to FIG. 4, block 310can define the upper limit 404 and lower limit 406 to bound N2 relativeto keep out zone width 408. Block 312 can compute the adder authority asδ_(ADDER). Block 314 can define the closing threshold 412 and openingthreshold 414 consistent with the adder authority and k. Block 316 candetermine the projected state of N2 as N2−k*δ_(ADDER). The actuationcontroller 304 can include a lead/lag filter 320 to filter a value of N2feedback 322, which can be a sensed value of N2. Further, the lead/lagfilter 320 may be omitted in embodiments. An N2 value (e.g., a filteredor unfiltered version of N2 feedback 322) can be passed to a closingkeep out zone proportional-integral control 324 and an opening keep outzone proportional-integral control 326. Block 310 can provide upperlimit 404 to the closing keep out zone proportional-integral control 324and lower limit 406 to the opening keep out zone proportional-integralcontrol 326. The actuation controllers 304 can apply the closing keepout zone proportional-integral control 324 to N2 feedback 322 withrespect to the upper limit 404 and a range limit 328 to determine aclosing correction 330. The actuation controllers 304 can also apply theopening keep out zone proportional-integral control 326 to the N2feedback 322 with respect to the lower limit 406 and a range limit 332to determine an opening correction 334.

The final selection logic 306 can include a multiplexer 336 to selectbetween the closing correction 330 and the opening correction 334 basedon a flag value set by block 318 to produce a correction command 338that can be further constrained by rate limiting 340 to prevent largerstep changes. The output of the rate limiting 340 is an adder value 342that can be combined at summing junction 344 with a high pressurecompressor stator vane schedule 346 to produce a high pressurecompressor stator vane request 348 to control a position of a pluralityof high pressure compressor stator vanes using the high pressurecompressor stator vane actuator 230 of FIG. 2.

Referring now to FIG. 5 with continued reference to FIGS. 1-4, FIG. 5 isa flow chart illustrating a method 500 for keep out zone control, inaccordance with an embodiment. The method 500 may be performed, forexample, by the control system 200 of FIG. 2. For purposes ofexplanation, the method 500 is described primarily with respect to thecontrol system 200 of FIG. 2; however, it will be understood that themethod 500 can be performed on other configurations (not depicted). Themethod 500 can be applied for a spool, such as the high speed spool 32,where primary speed control of the gas turbine engine 20 is performedwith respect to the low speed spool 30 and secondary control of the highspeed spool 32 is constrained by commands targeting performance of thelow speed spool 30.

At block 502, the controller 256 can determine a closing threshold 412with respect to an upper limit 404 and an opening threshold 414 withrespect to a lower limit 406 of a movement range of an effector of thegas turbine engine 20 based on an on-board model as part of themodel-based keep out zone control 266, where the upper limit 404 and thelower limit 406 define a keep out zone of a target parameter of the gasturbine engine 20. The effector can be a high pressure compressor statorvane actuator 230 and the target parameter can be N2, as an example. Atblock 504, the controller 256 can determine a projected state of thetarget parameter of the gas turbine engine 20 absent application of acorrection command 338 to the effector. For example, when the addervalue 342 is nonzero and the design is active, block 316 can project astate of N2 in steady state if the adder value 342 was zero to predictN2 without the effect of applying the actuation controllers 304. Thecontroller 256 can apply a closing keep out zone proportional-integralcontrol 324 to the target parameter (which may be filtered) with respectto the upper limit 404 to determine the closing correction 330. Thecontroller 256 can apply an opening keep out zone proportional-integralcontrol 326 to the target parameter with respect to the lower limit 406to determine the opening correction 334.

At block 506, the controller 256 can apply a closing correction 330 tothe effector as the correction command 338 based on determining that theprojected state of the target parameter of the gas turbine engine 20would result in being above the closing threshold 412. At block 508, thecontroller 256 can apply an opening correction 334 to the effector asthe correction command 338 based on determining that the projected stateof the target parameter of the gas turbine engine 20 would result inbeing below the opening threshold 414. The closing threshold 412 and theopening threshold 414 can define a switch hysteresis band 410, and theupper limit 404 and the lower limit 406 can define a keep out zone width408 with respect to the target parameter of the gas turbine engine 20.

The controller 256 can select between the closing correction 330 and theopening correction 334 based on comparing the projected state of thetarget parameter with the closing threshold 412 and the openingthreshold 414 to determine the correction command 338. The correctioncommand 338 can be added to a high pressure compressor stator vaneschedule 346 to control a position of a plurality of high pressurecompressor stator vanes using the high pressure compressor stator vaneactuator 230. The correction command 338 can be rate limited by ratelimiting 340, and the closing correction 330 and the opening correction334 can be range limited by range limits 328, 332. The controller 256can determine an adder authority to define the upper limit 404 and thelower limit 406 based on at least one speed and at least one vane angleof the gas turbine engine 20. The adder authority, which is how much theeffector can change the target, can be split between an openingdirection and a closing direction of the effector as adder value 342.The closing threshold 412 and the opening threshold 414 can bedetermined with respect to the adder authority, a change rate of the atleast one speed (e.g., N2), and a change rate of the at least one vaneangle (e.g., of the high pressure compressor 52). The projected state ofthe target parameter can be determined based on a value of the at leastone speed, the adder value 342, the change rate of the at least onespeed, and the change rate of the at least one vane angle.

While the above description has described the flow process of FIG. 5 ina particular order, it should be appreciated that unless otherwisespecifically required in the attached claims that the ordering of thesteps may be varied. Also, it is clear to one of ordinary skill in theart that, the stability enhancement provided by the dynamic torque andpower capability of the coupled electric motor system described hereincan be combined with and enhance other surge control features, such assurge control valves, variable stators, and fuel flow control.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A system for keep out zone control comprising: agas turbine engine comprising at least one compressor section and atleast one turbine section operably coupled to a shaft of a spool; and acontroller operable to: determine a closing threshold with respect to anupper limit and an opening threshold with respect to a lower limit of amovement range of an effector of the gas turbine engine based on anon-board model, wherein the upper limit and the lower limit define akeep out zone of a target parameter of the gas turbine engine; determinea projected state of the target parameter of the gas turbine engineabsent a correction command to the effector; apply a closing correctionto the effector as the correction command based on determining that theprojected state of the target parameter of the gas turbine engine wouldresult in being above the closing threshold; and apply an openingcorrection to the effector as the correction command based ondetermining that the projected state of the target parameter of the gasturbine engine would result in being below the opening threshold.
 2. Thesystem of claim 1, wherein the closing threshold and the openingthreshold define a switch hysteresis band, and the upper limit and thelower limit define a keep out zone width with respect to the targetparameter of the gas turbine engine.
 3. The system of claim 1, whereinthe spool is a high speed spool, and the gas turbine engine furthercomprises a low speed spool, wherein the low speed spool comprises a lowpressure compressor section and a low pressure turbine section.
 4. Thesystem of claim 3, wherein the target parameter is a speed of the highspeed spool, and the effector is a high pressure compressor stator vaneactuator.
 5. The system of claim 4, wherein the controller is furtherconfigured to: select between the closing correction and the openingcorrection based on comparing the projected state of the targetparameter with the closing threshold and the opening threshold todetermine the correction command; and add the correction command to ahigh pressure compressor stator vane schedule to control a position of aplurality of high pressure compressor stator vanes using the highpressure compressor stator vane actuator.
 6. The system of claim 5,wherein the correction command is rate limited, and the closingcorrection and the opening correction are range limited.
 7. The systemof claim 1, wherein the controller is further configured to: determinean adder authority as an adder value to define the upper limit and thelower limit based on at least one speed and at least one vane angle ofthe gas turbine engine; and split the adder value between an openingdirection and a closing direction of the effector.
 8. The system ofclaim 7, wherein the closing threshold and the opening threshold aredetermined with respect to the adder value, a change rate of the atleast one speed, and a change rate of the at least one vane angle. 9.The system of claim 8, wherein the projected state of the targetparameter is determined based on a value of the at least one speed, theadder value, the change rate of the at least one speed, and the changerate of the at least one vane angle.
 10. The system of claim 1, whereinthe controller is further configured to: apply a closing keep out zoneproportional-integral control to the target parameter with respect tothe upper limit to determine the closing correction; and apply anopening keep out zone proportional-integral control to the targetparameter with respect to the lower limit to determine the openingcorrection.
 11. A method for keep out zone control in a gas turbineengine, the method comprising: determining a closing threshold withrespect to an upper limit and an opening threshold with respect to alower limit of a movement range of an effector of the gas turbine enginebased on an on-board model, wherein the upper limit and the lower limitdefine a keep out zone of a target parameter of the gas turbine engine;determining a projected state of the target parameter of the gas turbineengine absent a correction command to the effector; applying a closingcorrection to the effector as the correction command based ondetermining that the projected state of the target parameter of the gasturbine engine would result in being above the closing threshold; andapplying an opening correction to the effector as the correction commandbased on determining that the projected state of the target parameter ofthe gas turbine engine would result in being below the openingthreshold.
 12. The method of claim 11, wherein the closing threshold andthe opening threshold define a switch hysteresis band, and the upperlimit and the lower limit define a keep out zone width with respect tothe target parameter of the gas turbine engine.
 13. The method of claim11, wherein the gas turbine engine comprises a high speed spool and alow speed spool, the high speed spool comprising at least one compressorsection and at least one turbine section operably coupled to a shaft,and the low speed spool comprising a low pressure compressor section anda low pressure turbine section.
 14. The method of claim 13, wherein thetarget parameter is a speed of the high speed spool, and the effector isa high pressure compressor stator vane actuator.
 15. The method of claim14, further comprising: selecting between the closing correction and theopening correction based on comparing the projected state of the targetparameter with the closing threshold and the opening threshold todetermine the correction command; and adding the correction command to ahigh pressure compressor stator vane schedule to control a position of aplurality of high pressure compressor stator vanes using the highpressure compressor stator vane actuator.
 16. The method of claim 15,wherein the correction command is rate limited, and the closingcorrection and the opening correction are range limited.
 17. The methodof claim 11, further comprising: determining an adder authority as anadder value to define the upper limit and the lower limit based on atleast one speed and at least one vane angle of the gas turbine engine;and splitting the adder value between an opening direction and a closingdirection of the effector.
 18. The method of claim 17, wherein theclosing threshold and the opening threshold are determined with respectto the adder value, a change rate of the at least one speed, and achange rate of the at least one vane angle.
 19. The method of claim 18,wherein the projected state of the target parameter is determined basedon a value of the at least one speed, the adder value, the change rateof the at least one speed, and the change rate of the at least one vaneangle.
 20. The method of claim 11, further comprising: applying aclosing keep out zone proportional-integral control to the targetparameter with respect to the upper limit to determine the closingcorrection; and applying an opening keep out zone proportional-integralcontrol to the target parameter with respect to the lower limit todetermine the opening correction.